Railway traffic controlling apparatus



Jan. 1, 1935. 1 v. LEWIS RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Aug. 2, 1927 Patented Jan. 1, 1935.

RAILWAY TRAFFIC vcon'rnontnv APPARATUS Y Lloyd V. Lewis, Edgewood Borough, Pa., assigner to' The ,Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application August 2, 1927, Serial No. 210,165

50 Claims.

-5. trackway.

`The present case is a continuation-in-part of my co-pending application, Serial No. 116,608, led June 17, 1926, for Railway traflic controlling apparatus, now Patent 1,824,605 of Sept. 22, 1931.

I will describe one form of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig.'4 1 is a diagrammatic View illustrating one form of trackway apparatus embodying my invention. Figs. 2, 3 and 4 are sketches illustrating the operation of certain portions of the apparatus of Fig. 1 when subjected to shock excitation. Referring first to Fig. 1, the Vreference characvters 1 and 1a designate the track rails of a stretch of railway track over which trafiic moves in the direction indicated by the arrow. These rails are dividedby means of insulated joints 2 into a plul rality of successive tracksections, of which only `one section, A-B, is shown complete in the drawing. Train controlling current is supplied to the rails of this section from a suitable source of en- Y ergy such as an alternator AM. Thev current supf plied to the trackway by this alternator may be of la frequency of the orderof the usual commercial alternating Y current, suchv for example, as 60 cyclesfor 100 cycles per second.

The supply of` current to the' track rails is controlled by a code ltransmitting device comprising .a plurality of vrotatable cams -each designated by the reference character O with a suitable distinguishing exponent. The cams O are driven at a constant speed by a suitable motor J which is supplied with current from the alternator M. The cam Ol is provided with a plurality ofswells 5 spaced about its periphery, which swells suc- U cessively operate a contact 6 to periodically close the contact as the cam O1 is rotated. In similar manner the cams O2 and O3 are provided with diierent numbers of swells 5 which control contacts '1 and 8, respectively. One terminal of the alternator M is constantly connected with rail 1v of section A-B, andthe other terminal of th'e alternator is connected with the rail 1a through a current limiting impedance Z, and one of the contacts 6, 7 or 8, depending upon traffic conditions.

It is manifest that the alternating current supplied to the rails of4 the trackway by alternator M is coded or periodically varied at the frequency of operation of the contact of the code transmit- (c1. 24e-63) i ting device interposed between the alternator and the track rail la. The code transmitting device may be constructed to cause such variations at any reasonable frequencies, but for purposes of illustration, I will assume that the cams O are rotating at 20 revolutions per minute, that cam O1 has 4 swells, that cam O2 has 6 swells, and 'that cam O3 has 9 swells. The selection between th several contacts of the coding device in accordance with traffic conditions may be accomplished 10 in any suitable manner such, for example, as by means of a home relay 3 and a distant relay 4.

l The circuits for controlling these two relays form no part of my present invention and are omitted from the drawing for the sake of simplicity. For l5 present purposes, it is suicient to state that home relay 3 is normally energized but is deenergizedv when a train occupies the section immediately to the right of point B. The distant relay 4 is also 'normally energized but is de-energized when a 20 train occupies either the rst or the second section immediately to the right of point B. When relays 3 and 4 are both energized, so that the front contacts of both thse relays are closed, current from alternator M, which current I will as- 25 sume to be of cycles .per second, is supplied to the track rails over contact 8 operated by cam O3. Under. these conditions, the alternating current supplied to the trackway is periodically varied at a frequency of 180 cycles per minute. Current 30 supplied to the trackway-under these conditions,

I will hereinafter term the clear code. When relay 3 is energized and relay 4 is deenergized, contact 7 controlled by cam O2 is included in the trackway circuit, and under these conditions the 35 trackway is supplied with 100 cycle current interruptedat a frequency of cycles per minute; this current I shall hereinafter term the approach restricting code. `In similar manner, when relay 3 is de-energized, a circuit is com- 40 pleted from alternator M tov the track rails through contact 6 operated by 'cam O1, and the trackway is then supplied with 100 cycle current interrupted at a frequencyof 80 Acycles per minute, which current I will call the approac 45 code.

A train, indicated diagrammatically at V, is provided with a receiver designated in general by the reference character P. This receiver comprises two magnetizable cores 22 and 22a, carried 50 on the train in advance of the forward axle, and located in inductive relation with the two track rails. 1 and l, respectively. Core 22 is provided with a winding 23, and core 22 is provided with a. similar winding 23; the windings 23 and 23a 55 elements, which I will term the "pick-up circuit,

is tuned to resonance at the frequency of the alternating current in the trackway. The secondary circuit of the auto transformer L is tuned to' resonance at the frequency of this .current by a condenser 26. 'I'he periodically Varying 100 cycle voltage across the terminals of condenser 2,6 is first amplied and then detected or converted to low frequency alternating current by two electron tube ampliers E1 and E2. The laments of these tubes are connected in a series circuit including a ballast lamp 11 and two control resistances 10 and 12, and this circuit is supplied with current from a suitable source such as a battery 9. The secondary of the auto transformer L and the condenser 26 in parallel therewith, are

' connected across the grid and filament of the` tube E1 and also across the resistance 10 in thev filament circuit, so that the grid is normally neg- 'ative" by several volts with respect to the lament of E1. 'The rst stage or amplier tube E1 is provided with a plate circuit including a suitable source of high potential unidirectional current -such as a battery 13, primary 14 of an interstage transformer K, the plate and filament of the tube E?, and the resistance v10. The second stage or detector tube E2 is provided with a plate circuit including the battery 13 and the primary 16 of a low frequency transformer Y. Secondary 15 of transformer K is connected across the-grid and lament of-tube E2 in such manner that the grid normally, when no 100 cycle voltage is present, has a suicient negative bias so that the plate current of tube E2 is substantially zero. The secondary 17 of transformer Y is connected directly with a polarized relayD, that is, a relay which is selectively responsive to the polarity of the current supplied thereto. N

When any code is being supplied to the trackway, the 100 cycle energy picked up by receiver P, after passing through the ltering apparatus comprising transformer L, is applied to the grid circuit ofl tube E1. Amplified 100 cycle current of periodically varying amplitude-of a value which dependsnpon the electromotive force across winding N, and consequently upon the value and rate of interruption of the trackway current, will be delivered by tube E1 to the primary of transformer K, and the secondary of this transformer will supply an alternating voltage of corresponding value to the grid. circuit of tube E2. Due to the comparatively high impedance of primary 16 of transformer Y, substantially no current of 100'cycles ows through the plate circuit of tube E2. It will be noted, however, that the normal bias of the grid of tube E2 is negative so that the normal plate current through this tube is comparatively low. When the 100 cycle current is being supplied to the trackway, however, the alternating voltage supplied by the secondary of transformer K is superimposed' upon this ilxed voltage and is rectiied and decreases the negative charge u pon thegrid of tube E2, causing a proportionate increase in the plate current of tube E2. When the 100 cycle voltage is cut oil?, that is, when the track- Way current is interrupted, the plate current of tube E2 is restored to its original value. It follows that when a code is being supplied to the trackway the plate current of tube E2 is periodically increased and decreased at the same frequency as the periodic variations of the trackway current. Each increase in current through primary 16 of transformer Y induces in secondary17a current impulse which energizes a two-position polarized relay D in one direction, and each decrease of current in primary 16 induces a current impulse in secondary 17 which energizes relay D inthe opposite direction. As a result, relay D is operated alternately, first in one direction, and

A then in the other, by low frequency impulses alto the other when the current through its winding derived from the trackway currentv detected by tube E2 is of a suiicient value to overcome the pull of the permanent magnet on the armature.

Although the relay D faithfully follows the periodic variations in the trackway current when the value of this current exceeds a predetermined minimum, the relay cannot be alternately operated by energy' supplied tothe train carried circuits by shock excitation, that is, by free oscillations in the ltering apparatus including the auto transformer L, of the frequencyto which the ltering circuits are resonant. Such excitation may be caused, for example, by sudden changes in director alternating currents in the trackway or from any source in the vicinity of the train carried apparatus. The wave front of the exciting current may be very steep, that is, the current change which causes the free oscillations may be very rapid, and. as a result there may be induced in the lter circuits a surge of current which supplies a surge of alternating voltage to the grid circuit of tube E1. Oscillograph analysis of these free oscillations shows V filter circuits is similar to that shown in Fig. 2.

It will be observed from this diagram that a considerable greatertime is required for the surge to die down than for the surge to build up to its maximum value. For example, if 4 cycles are required for the free oscillations to reach their maximum amplitude, 8 cycles or more may be required before these oscillations die out. But as has already been explained, an increase of current in the grid circuit of tubeE1 increasesthe plate current in tubeI E2. It follows; that this plate current varies as shown in Fig. 3 when free oscillations of Fig. 2 are created in the filter circuits. 'Ihe rate of change of this plate current is, of course, much more rapid during the growth of the free oscillations than during the decay of suchoscillations.

Referring now to Fig'. 4, the increase in the plate current of tube E2, due to the growth of the free oscillations, induces in secondary 17 an impulse of energy represented by the loop 138 which energizes the relay D in one direction. The value of energy necessary to operate the relay in such one direction is represented by line 135 above the zero axis 137, and the value of energy necessary to operate the relay in the opposite direction is represented by a line 136 below the'zero axis 137. It is apparent that by properly proportioning the various parts,-the relay may be so constructed that while it may operate' tion in the trackway current. ,As a result of this, `there is induced in the secondary 20A avlow fre-y ates.

sented by'loop138,'the impulse of energy represented by loop 139 caused by the gradual return of the plate current of tube E1 to its normal value, during the dying out of the free oscillations, will not be suflicient to operate the' relay in the other direction.

Since the relay D remains in the position to which it was last positively moved, it follows that with the partsarranged in this manner, shock excitation cannot cause a complete cycle of operation of relay D, but the first shock impulse will cause relay D to move from normal to reverse while subsequent shock impulses will merely hold it in the reverse position. 'l

The relay D controls decoding apparatus which is selectively responsive to the frequency of operation of the relay. In the present embodiment of my invention, this apparatus is constructed as follows:

Associated with relay D is a transformer T comprising a primary 19 and Va secondary v20. Direct current is supplied to the primary 19 of transformer T from a suitable source of energy i such as a battery 28, and the supply of such current is periodically varied in direction in accordance with the frequency at which relay D oper- As shown in the drawing, when relay D is energized in one direction to close contact 18-18, current flows fromgbattery 28 through the lower half of primary 19 in one direction, but when the relay D is energized in the oppositedirection so that contact 18--18b is closed, current flows from `battery 28 through the upper half 4of primary` 19 in the opposite direction. It followsthat when relay D is periodically reversed by the low frequency alternations in polarity of the current delivered by transformer Y, these alternations will be repeated by relay D and the current in primary 19 of transformer T will be periodically reversed at the frequency of the periodicvariaquency alternating electromotive force which is supplied to a plurality of circuits each designated by the reference character C with a distinguishing exponent, and each comprising a reactor 24 and a condenser 21, by means of which the several circuits are tuned, respectively, to the several code frequencies. For example, circuit C3 is tuned to resonance at the frequency' of the clear code or 180 cycles per minute. A clear or proceed train control relay R3' is connected across a portion of reactor 24 of circuit C3 through a rectifier h3, and is arranged to be energized only when the relay D is operated by a 180 cycle code picked up from the trackway. In similar manner, circuit C2 is tuned toresonance at 120 cycles per minute and a caution train `control relay R2 is connected across av portion of reactor 24 of this circuit through a rectifier h?. Relay R2 is arranged lto be energized only when relayD is operated by a cycle` code picked up from ,the trackway. A slow speed train control relay l' R1 is connected, through rectifier h1 and reactor 27, directly withsecondary 20,0f transformer T,

and relay R1 is arranged to be energized when relay D is receiving any fthel train control code frequencies. The relays R are `thus rendered se.

lectively responsive to the frequenc of the trackway currents, andare inthismanner caused to be continuously responsive to tramc conditions in advance of the train, and these relays control visual cab signals comprising the series of lamps 41 to 44, inclusive.

l.Associated with the relaysl R are a plurality of normally deenergized retaining relays or stick relayseach designated by the reference character S with a distinguishing exponent. The relays R -and S may control governing means of any suitable type, which as here shown is winding 455 of a magnet valve G arranged when energized to connect a reservoir 29 with a suitable source of fluid pressure not shown in the drawing. The reservoir 29 is connected with a relay valve H so that when this reservoir is charged valve H Aoccupies the position shown in the drawing and a pneumatic relay 31 is connected by pipe 12B with a source of fluid pressure so that contact 32 of this relay is closed. Pipe 128 controls also a brake application valve (not shown) for causing anapplication of the brakes when this pipe is connected to atmosphere. When winding 55 of valve G becomes de-energized, the reservoir 29 :is connected with atmosphere through a restricted orice 34 and also through a whistle 33 which serves as a warning signal and sounds to give to the engineman an audible indication withinthe cab of a change in trailic conditions to a more restrictive condition. After a` brief interval of time, such, for example, as 6 seconds, the pressure in reservoir 29 is so reduced that piston 30 of valve H-reverses, thereby venting At the same time the reversal of valve H connects the pneumatic relay 31 with atmosphere,

' opening the normally closed contact 32. If magpipe 128 to atmosphere and applying the brakes. Y

operable circuit. controller or acknowledging switch a located at some convenient place in the cab within the reach of the engineman, xand comprising a normally closed contact 52 and a normally open contact F11. When the acknowledging switch is reversed, contact 52 is opened, and contact 'Il is closed. Furthermore, a reset switch, designated by the reference character r, and comprising a normally closed contact 53 and a normally open contact 106, is provided, and located outside the cab Where it will be inaccessible to the engineman when the train isin motion.

.In explaining the operation of `the apparatus as a whole, I will first assume that the clear code is being supplied to the trackway so that the trackway current is being interrupted atthe frequency of cycles per' minute.; Relay D therefore operates at the rate of 180 cycles per minute and alternating current of a corresponding frequency is supplied by secondary 20 of transformer T. Relays R1 and R3 are therefore energized, but relay li',2 is de-energized because the circuit Czis not resonant at the frequency of thel current now supplied to such circuit. With relay R3 energized,`current flows from battery 28, through wires 37 and 38, front contact 39 of relay R3, wire 40, lamp 41, wire 45, front contact 46 of relay R3, and wires 47 and 48, back to battery 28. 'Ihe lamp 41- is therefore lighted to indicate clear or proceed,V At the same time, current flows over the circuit just traced as far as wire 40, and thence through Wire 49, back contact 50 of relay S3, wire 51, contact 52 of acknowledging switch a, contact 53,0f the reset switch r, wire 54, winding 55 of magnet'valve G, wire 56, back contact '57 of rereduction of pressure in reservoir 29,' and to cause the whistle 33 to sound. Current now flows from battery 28, through wires 37 and 38, back contact 39 of relay R3, Wires 59 and 60, front contact 61 of relay R2, wire 62, lamp 42, wire 63', front contact 64 of relay R2, wires 65 and 66, back contact 46 of relay R3 and wires 47 and 48 back to battery 28. The lamp 42 therefore becomes energized to indicate approach restricting or caution and, by the change of visual indication, to inform the engineman that upon the expiration of the time interval required for the blow-down of reservoir 29, an automatic application of the brakes will result. If, however, prior to the reversal of valve H the. engineman operates the acknowledging switch a, he may forestall an automatic application of the brakes in the following manner:

When contact 71 of switch a is closed, current iiows from battery 28, over wires 37 and 38, back contact 39 of relay R3, wires 59, 67, 68 and 69, contact 32 of pneumatic relay.31, wire 70, contact 71 of acknowledging switch a, wires 72, 73 and 74, winding of relay S1, wires 75, 81, 76 and 66, back contact 46 of relay R3, and wires 47 and 48, back to battery. 28. Relay S1 therefore rbecomes energized and closes a pick-up circuit for relay S2 from battery 28, over Wires'37 and.

38, back contact 39 of relay R3; wires 59, 67 and 77, front contact 78 of relay S1, wire 79, winding 35 of relay S2, wires 80, 81, 76 and 66, back 'contact 46 of` relay R3, and wires 47 and 48 back to battery 28. Relay S2 therefore picks up. The closing of front contact 82 of relay S2 completes a pick-up circuit for relay S3, from battery 28 over wires 37 and 38, back contact 39 of relay R3,

wires 59, 67 and 68, front contact 82 of relay S2,

wire 83, winding 35 of relay S3, wires 84, 85,. 76 and 66, back contact 46 of relay R3, and wires 47 and 48, back to battery 28. 'Ihe relay S3 therefore closes its front contacts. When front contact 87 of relay S3 becomes closed, a. stick circuit is closed for this relay from battery 28, over wires 37 and 38, back contact 39 of relay R3, wires 59 and 60, front contact 61 of relay R2, wires 62 and 86, front contact 87 of relay. S3, wire 88, winding 36 of relay S3, wires 85, 76 and 66, back contact 46 of relay R3, and wires 47 and 48, back to battery 28. A'I'he acknowledging switch a may now` be restored to its original position, thereby closing contact 52 and opening contact 71. The circuit for relay S1 is therefore opened and this relay becomes de-energized, and the opening of contact 78 thereon de-energizes relay S2. When contact 82 of relay S2 opens, the piek-up circuit including winding 35 of relay S3 becomes deenergized, but relay S3 maintains its front contacts closed by virtue of the stick circuit including winding 36 of this relay. With relay S3 energized and contact 52 of switch a closed, current from battery 28 flows over Wires 37 and 89, front vcontact 50 of relay S3, Wire' 51, contact 52 of switch a., contact 53 of yswitch r,

,wire 54, winding 55 of magnet valve G, wire 56,' .front contact 57 of relay S3, and wires 90 and 48 back to battery 28. It follows therefore that when the train is receiving the approach restricting code, and if the engineman has acknowledged the change in trame conditions from clear" to approach restricting the` relay S3 will be held energized and the magnet valve G will be energized to prevent an automatic application of the brakes.

It should be pointed out that after operation of the acknowledging switch a to close contact 71, the acknowledging switch must be again restored to its original position to 'close contact 52 after relay S3 has been picked up, in order to permit the magnet valve G to become energized.

Furthermore, if the acknowledging switch a is not operated before valve H reverses, the operation of the acknowledging switch will be ineffective to prevent an automatic application of the brakes. The reason for this is that as soon as valve H reverses, the pneumatic relay 31 operates to open contact 32, but the contact 321s included lin the pickup 'circuit for relay S1 so that after this contact is open, manipulation of the acknowledging switch a cannot pick up relay S1, If valve H does reverse, the train must be brought to a full stop in order to enable the en'- gineman to operate the reset switch rbefore valve H can be restored. When switch r is operated,

a branch is closed from wire 69, through wire.v

105, contact 106 of releasing switch rand wire 107 ba'ck to wire 73. It will be plain that the closing of contact 106 shunts current around the 'contact 32 of pneumatic relayl 31' and around contact 71 of the acknowledging switch a. When the reset switch r is operated, therefore, the replained for the operation of these relays upon manipulation of acknowledging switch a. When relay S3 has become energized, the reset switch 1' may be restored to its original position, thereby allowing relays S1 and S2 to drop. Relay S3 remains energized and magnet valve G becomes energized in the manner already described.

I will next assume that a change to a more re. stricting trailc condition occurs, so that the approach or slow code is Asupplied to the trackway. Relay R2 opens, but relay R1 is still energized by the current o'f 80 cycles per minute which is now supplied to it by transformer T. The de-energization of relay R2 interrupts the circuit for lamp 42 and alsobreaks the stick circuit for relay S3. 'The relay S3 therefore becomes 'deenergized, and opens the circuit for magnet valve G. The whistle 33 is therefore operated and the blow down of reservoir 29 is initiated so that an automatic application of the brakes will result at the expiration of a .time interval unless the engineman acknowledges. The necessity for this acknowledgment is indicated by the extinguishment of lamp 42 and also by the lighting of lamp 43, which latter is now energized by current which flows from battery 28 over wires 37 and 33, back 'contact 39 of relay R3, wires 59 and. 60, back contact 61 of relay R3, wire 91, front contact 92 of relay R1, wire 93, lamp 43, wire 94, front contact 95 of relay R1, Wire 96, back contact 64 of relay R2, wires 65 and 66, back contact 46 of relay R3 and wires 47 andv 48 back to battery 28. Y

1f the engineman wishes to forestall an automatic application of the brakes, he operates the acknowledging switch a before valve H reverses.

guishes lamp 44 and opens the stick circuit for Since relay R3 is cle-energized, the closing of the contact '71 completes the-circuit for relay S1 and this relay picks up, and in turn closes the circuit for winding 35 of relay S2. Furthermore, the closingv of contact 82 of'relay S2 picks up relay S3. Acknowledging switch a can now be restored to its original position. When this happens, the opening =of contact '11 opens the circuit for relay S1 and this relay becomes de-energized. Relay S2, however, is held in its energized position by current which flows from battery 28 over the circuit already traced for lamp 43 as far as wire 93,

and thence overwire 97, front contact 98 of relay S2, wire 99, winding 36 of relay S2, wires 81, '76 and 66, back'contact 46 of relay R3 and wires 47 and 4s back to battery 2s.' Reny S215 therefore Aheld closed as long'as the approach code is received on board the train. With contact 82 of relay S2 closed, relay S3 is also energized and since contact 52 is closed, the magnet valve G- is also energized over front contacts 50 and 5'?` of relay S3, to prevent an automatic application of the brakes. It should be pointed out that should the relay 31 open its contact before the engineman actuates the acknowledging switch a, the acknowledgment will be ineifective and he must bring his train to a full stop and operate the reset switch r to pick up the stick relays S.

I will now assume that the track circuit current is cut olf to give the most restrictive or stop indication of the system, which indication is given under danger conditions and is usually designated as caution slow speed. Relay D does not periodically reverse and relays R3, R2 and R1 are therefore all de-energized, lamp 43 becomes extinguished, and the stick circuit for relay S2 is opened. Relay S2 therefore becomes de.enerm gized, and the opening of front contact 42 thereon de-energizes relay S3. The magnet valve G is therefore de-energized to commencethe blow down of reservoir 29 and to'sound the ywhistle 33.

`3'? and 438, back contact 39 of relay R3, wires 59 and 60, back contact 61 of relay R2, wire 91, back contact 92 of relay R1, wire 100, lamp 44, wire 101, back contact 95 of relay R1, wire 96, back contact 64 of relay R2, wires 65 and 66, back contact 46 of relay R3 and wires 47 and 48 back to battery 28. If the engineman wishes to acknowledge the change in traflic conditions to prevent an automatic application of the brakes, he operates the acknowledging switch a. The relays S1, S2 and S3 are therefore picked up in sequence. The engineman then restores the acknowledging switch to its original position. Relays S1 is now maintained in its energized condition by current which flows over the circuit for lamp 44 as far as wire 100, and thence through wire 102, front contact 103 of relay S1, wires 104 and '74, winding of relay S1, wires "I5, 8l, '16 and 66, back contact 46 of relay R3 and wires 47 and 48 back to battery 28. Relay S1 therefore remains in its energized condition and since contact 78 of this relay is closed, relay S2 is also picked up, andl relay S3 is energized over front contact 82 of relay S2. The magnet valve G is therefore energized by current from battery 28 over the circuit including front contacts 57 and 58 of relay S3.

Should traiic conditions now become less restrictive and change in such manner that the approach code is supplied to the trackway, relay R1 becomes energized and relays R2 and R3 remain de-energized. The energization of relay R1 completes the circuit for'lamp 43 and extin- S3 and does not de-energize magnet valve G.

Upon a change in traffic conditions from the caution slow fspeed" to the "approach therefore, no acknowledgment is necessary upon the part of the engineman to prevent an automatic application of the brakes.

If now tramo conditions become still less restrictive and change from approac to the approach restricting condition, relay R2 becomes energized. The energization of relay R2 extinguishes lamp 43 and completes the circuit for lamp V42 and breaks the stick circuit for relay S2 at back contact 61 of relay R2. The stick relay S2 therefore opens, but the stick circuit for relay S3 is nowclosed at front contact 61 of relay 'R2 and front contact 87 of relay S3. The relay S3 therefore holds its front contacts closed and Aapproach to approach restricting.

Finally, i-f the clear condition is re-established, relay R3 becomes energized. Lamp 42 is therefore extinguished and lamp 41 is lighted. The stick circuit for relay S3 is also broken so that relay S3 becomes de-energized. But with relay R3 energized and with relay S3 de-energized, current is supplied from battery 28 to winding 55 of magnet valve G, over front contacts on relay R3 and back contacts of relay S3 so that no automatic application of the brakes results from a change in traine conditions from approach restricting to clear. Furthermore, if the whistle is sounding, it is evident that its operation will be automatically interrupted upon a change to clear trailic conditions.

In conclusion, it should be pointed out that not only does the visual signal continuously indicate within the cab the condition of the track in advance, but theapparatus is arranged in such manner that upon' any change in traiiic condition from a less restrictive to a more restrictive indication, an audible warning signal is sounded, and an automatic application of the brakes will result unless the engineman operates the acknowledging switch a during the time interval required for the blow down of reservoir 29. Upon any change from a more restrictive to a less restrictive indication howeventhe magnet valve G does not 'become de-energized and no acknowledgment by the engineman is necessary.

Relays S1, S2 and S3 are slightly slow acting, in order that momentary opening of the circuits for these relays, as during the -reversal of a relay R, will not compel acknowledgment of a change from a more restrictive to a less restrictive indication.

It will be apparent from the foregoing explanation that in order to give any indication on board the train except the caution slow speed indication represented by the lighting of lamp 44, it is necessary that relay D be energized alternately. But this alternate operation of relay D cannot be accomplished as a result of shock excitation. It follows that under no condition can a false indication be received upon the train as a result of shock-excitation.

Another Vadvantage possessed by the apparatus shown inthe drawing, ,is that since relay D requires for its operation a reversal of the polarity of the current supplied thereto, there will be much less variation in the relative lengths of time that a contact of the relay is opened and closed due to variations in Jthe magnitude of the impulses delivered to the relay than would be the case if a neutral relay were employed in place of relay D. This is due to the fact that in normal operation the current supplied to relay D is alternating, and the reversals of the relay are uniformly spaced, since they occur at corresponding current values of opposite polarity, irrespective of the magnitude of the impulses, whereas a neutral relay which picks up and releases as its current exceeds or drops below fixed values of the same polarity will have its timing materially changed by a variation in the magnitude of the impulses.

I do not claim as my invention the combination of a stretch of track supplied with alternating current periodically varied at different frequencies, a master relay'on the train operated at the rate of such periodic variations, and train car- ,ried relays controlled by the master relay and selectively responsive to the rate of operation of the master relay, such combination being disclosed and claimed'in the following applications for Letters Patent of the United States: L. L. Lockrow,

Serial No. 166,395, led February 7, 1927, nowv 1927, now Patent No. 1,773,515, granted Aug. 19,

1930, for Railway traic controlling apparatus.

' Although I have herein shown and described only one form of railway traflic controlling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

' Having thus described my invention, what I claim is:

1. In combination, a stretch of railway track, means for supplying the stretch with alternating current periodically varied at diierent frequencies, a train carried polarized relay, means controlled by the current in the trackway for supplying the relaywith impulses of energy ofV alternatelyv reversed polarity to operate the relay at the frequency of such variation, and governing means selectively responsive to the frequency of,

operation of the relay. 2. In combination, a stretch-of railway track, means 'for supplying the stretch with alternating current periodically varied at different frequencies, a train carried electron tube, means for varying the potential of the grid of such tube in accordance with such variations, a transformer, a plate circuit for the tube including the primary of the transformer, and afrelay connected with the secondary of such transformer and responsive to the polarity of the current supplied thereto. 3. In combination, a stretch of railway track, means for supplying the stretch with alternating current periodicallyr varied at different frequencies, a train. carried transformer having a primary supplied with unidirectional current, means for varying the magnitude of such unidirectional current at the frequency `of the variations in the trackway current, a polarized relay receivingenergy from the secondary of the transformer, and governing means selectively responsive to the frequency of operation of said relay.

4. In combination, a stretch of railway track', means for supplying the stretch with periodically varied alternating current, a train carried electron tube having a plate circuit, means for varying the current in such plate circuit in accordance with the variations in the trackway current, a polarized relay, means for energizing the relay alternately in opposite directions at a frequency depending upon the frequency of the variations in the plate circuit and governing means controlled by the relay and responsive to they frequency at which such relay operates.

5. In combination, a stretch of railway track, means for supplying periodically varying alternating current thereto, a train carried autotransformer having a secondary tuned to resonance at the frequency of such current, a pickup circuit receiving energy from the trackway and including a portion of the transformer and tuned to resonance at the frequency of such current, a first electron tube having a plate circuit, means for applying to the lament and grid of the rst tube an alternating potential which varies as the electromotive force of the secondary of the auto-transformer, a second electron tube having its grid circuit coupled with the plate circuit of the rst tube, a transformer, a plate circuit for the second tube including the primary of the transformer, a polarized relay connected with the secondary of the transformer, and governing means responsive to the frequency of operation of the relay.

6. In combination, a stretch of railway track, means for supplying the stretch with periodically varying alternating current, a train carried transformer having a primary supplied with current, means including a tuned circuit for varying the current in the primary in response to variations in the trackway current, and a relay connected with the secondary of the transformer and arranged to be operated in one direction by the energy. supplied thereto when the current in said primary is increasing and to be operated in the other direction by the energy supplied thereto when the current in said primary is decreasing but requiring'for operation in such other direction a greater electromotive force than is supplied thereto as a result of free oscillations in said tuned circuit caused by shock excitation.

7. Railway trafiic controlling apparatus comprising .a train 'carried relay, means located partly in the trackway and controlled by trailic conditions for at times energizing lsuch relay, a magnet valve on the train, a governing device controlled by the valve, a stick relay, a manually operable circuit controller having a normal and a reverse contact, a circuit for picking up said stick relay including a reverse contact of said circuit controller and a back contact of the train carried relay, a second circuit for said stick relay including its own front contact and a back contact of' the train carried relay; a circuit for said valve including a normal contact of said circuit controller, a back contact of the stick relay, and a front contact of the train carried relay; and a second circuit for said valve including a normal contact of the circuitcontroller, a front contact of the stick relay, and a back contact of the train carried relay.

8. Railway traii'ic controlling apparatuscomprising a series of train carried stick relays, manually operable means effective under certain traic conditions to energize the rst relay of said series, a pick-up circuit for each of the remaining relays including a front contact of the preceding relay-in said series, a stick circuit for each relay controlled in accordance with traiiic conditionsand governing means controlled by 'said stick relays.

prising three train-carried relays R1, R2 and R3,

means for energizing relays R1 and R3 under proceed conditions, means for energizing relays R1 and R2 under caution conditions, means for energizing relayfR1` under slow conditions, all such relays R1, R2 and R3 being de-energized under stop conditions, three stick relays S1, S2 and S3, an electromagnetic valve for controlling the brakes, a rst circuit for said valve including a front contact of relay R3 and a back contact of relay S3, a second circuit for said valve including a back contact ofrelay R3 and a front contact of relay S3, a manually operable contact, a pick-up circuit for relay S1 including said manually operable contact and a back contact of relay R3; a stick circuit for relay S1 including a front contact of relay S1 and back contacts on relays R1, R2 and R3; a pick-up circuit for relay S2 including a front contact of relay S1 and a back contact of relay R3; a stick circuit for relay S2 including a front contact of relay S3, a front contact of relay R1, and back contacts of relays R2 and R3; a pick-up circuit for relay S3 including a front contact of relay S2, and a back contact of relay.R3; and a stick circuit for relay S3 including a front contact of relay S3, a front contact of relay R2, and a back contact of relay R3.

1l. Railway trailc controlling apparatus comprising a train carried warning signal, a normally deenergized relay, means located partly in the trackway and eiective to prevent operation of the signal under certain traffic conditions if said relay is deenergized, manually operable Vmeans effective under certain other traflic conditions to energize the relay, and means effective under such other traffic conditions to prevent operation of said signal when said relay is energized.

12. Railway traiiic controlling appartus comprising a plurality of signals carried on the train, means located partly in the trackway and continuously responsive to traic conditions in advance of the train for energizing a selected one or another of said signals in accordance with tramc conditions, a whistle, means for operating said whistle upon a change in tralc conditions to a more restrictive condition, a manually operable circuit controller, and means operating if said circuit controller is reversed and then restored `to its normal condition to prevent operation of said whistle.

13. Railway traiic controlling apparatus comprising a visual cab signal controlled by traiic conditions in advance, an audible signal, means for operating said audible signal upon a change from a less to a more restrictive traflic condition,

manually operable means for preventing operation of said audible signal, and means for aut-omatically interrupting the operation of said audible signal upon a change from a more restrictive to a less restrictivey traiiic condition.

14. Railway traic controlling apparatus comprising three train-carried relays R1, R2 and R3, means for energizing relay R3 under proceed conditions, means for energizing relay R2 under caution conditions, means for energizing relay R1 under-slow conditions, all such relays R1, R2and` R3 being deenergized under stop conditions, three stick relays S1, S2 vand S3, an electropneumatic valve for controlling the brakes, a rst circuit for said valve including a front contact of relay R3, a second circuit for said valve including a front contact of relay S3, a manually operable contact, a pickup circuit for relay S1 including said manually operable contact, a stick circuit for relay S1 including a front contact of lrelay S1 and a contact closed only when relays R1, R2 and R3 are deenergized, a pickup circuit for relay S2 including a front contact of relay S1, a stick circuit for relay S2 including a front contact of relay S2 and a front contact of relay R1, a pickup circuit for relay S3 including a front contact of relay S2, and a stick circuit for relay S3 including a front contact of relay S3'and a front contact of relay R2.

15. Railway traffic controlling apparatus comprising a vehicle carried relay continuously responsive to trackway conditions and energized only under clear conditions, a normally energized magnet,- a circuit for said magnet including a front contact of the relay, mechanism for causing an automatic application of the brakes upon the vexpiration of aitirnainterval after deenergization of said magnet,a' normally closed contact arranged to open at the expiration of said time interval, an audible signal arranged to sound at the beginning: of ,'slaigl, time interval to attract attention to the deenilgizatiom of said magnet, and manually operable meanseffective only prior to the opening of said normally closed contact to reenergize said magnet,

16. Railway traic controlling apparatus comprising a vehicle carried relay continuously responsive to trackway conditions and energized only under clear conditions, a normally energized magnet, a circuit for said magnet including a front contact of the relay, mechanism for causing an automatic application of the brakes upon the expiration of a time interval after deenergization 'of4 said magnet, a normally closed contact arranged to open at the expiration of said time interval, an audible signal arranged to sound at the beginning of said time interval to attract attention to the deenergization of said magnet, cab-carried manually operable means eiective only prior to the opening of said normally closed contact for reenergizing said magnet, and other manually operable means inaccessible from the cab of the vehicle and independent of said contact for reenergizing. said magnet.

17. Railway traffic controlling apparatus com- I ing a front contact of the relay, mechanism forA causing an automatic application of the brakesv upon the expiration of a time interval after deenergization of said magnet, a normally closed contact arranged to open at the expiration of' said time interval, a stick relay, a switch inaccessible from the -cab`of the vehicle and manually operable to pick up said stick relay even though said normally closed contact is open, a cab-carried manual switch operable to pick up said stick relay only if said normally closed contact has not been opened, means for holding said stick relay energized when the front contact of the vehicle carried relay is open, and means ef- -fective when the stick relay is energized provided both said switches have been restored to their normal positions for preventing said mechanism `from causing an application of the brakes.

18. Railwaytraffic controlling apparatus comprising a vehicle carried magnet, mechanism for causing an automatic application of the brakes upon the expiration of an interval of time after deenergization of the magnet, a normally closed contact arranged to open at the expiration of such time interval, a vehicle carried relay continuously responsive to trackway conditions and arranged to be energized only under clear trac conditions, a circuit for said magnet including 'a front contact of'said relay, cab-carried manually controlled means including said normally-closed contact for at times shunting the front contact o'f the relay, and other manually'v controlled means inaccessible from the cab of the vehicle and independent of said normally closed contact for at times shunting the front contact of the relay.

19. Railway traflc controlling apparatus comprising a rst vehicle carried contact closed only under clear conditions of the trackway, and a. second vehicle carried contact closed only under caution conditions of the trackway, a magnet, a rst circuit for said magnet including said first contact, mechanism for causing an automatic application of the brakes upon the expiration of a time interval after deenergization ofk said magnet, a normally closed contact arranged to open at the expiration of said time interval, a first' and a.second stick relay, a holding circuit for the second stick relay including said second contact, a holding circuit for said rst'stick relay adapted to be closed only when said rst and second contacts are` open, a pickup circuit for the first stick relay including said normally closed contactand a manually operable switch, a pickup circuit for the second stick relay closed when the rst stick relay is energized, and a circuit for said magnet including a front contact of said second stick relay.

20. A railway cab signaling system comprising a vehicle, a train control relay controlled by current in the track rails and continuously respon.- sive to trackway conditions in advance of the vehicle, a visual cab signal controlled by said rel'ay comprising means /for indicating clear when said relay is energized and for indicating danger when said relay is deenergized, a uid pressure operated warning signal, a source of fluid pressure, means for connecting said source with said signal when the train control relay becomes deenergized, and manually operable means eiective when the train control relay is deenergized for discontinuing the supply of fluid pressure to said signal from said source although the train control relay remains deenergized.

21. Railway traiiic controlling apparatus comprising a train carried audible signal, a normally deenergized stick relay, a train carried relay continuously controlled by current in the track rails and responsive to trackway conditions in advance of the vehicle, means for preventing operation of said audible signal when said train carried relay is energized, manuallyI operable means effec- -tive under other conditions to energize said stick relay, and means effective when said stick relay is energized for preventing operation of said-audible signal.

22. Railway trac controlling apparatus comprising train carried means continuously responsive to .trackway conditions in advance of the train and `arranged to visually indicate a clear condition and a plurality of restrictive conditions of the track, an audible signal, means for causing said signal to operate upon a change from a clear condition to arestrictive condition of the track, means manually operable under a restrictive lcondition for stopping the operation of said audible signal while said restrictive condition exists, and means for causing said signal to again operate upon a'change from said restrictive condition to a different restrictive condition of the track.

23. Railway trailic controlling apparatus comprising train carried means continuously responsive to trackway conditions in advance of the train and arranged to visually indicate clear, caution, or danger condition of the track, an audible signal, means for preventing the operation of said signal under clear conditions, a rst and a second stick relay, manually controlled means operable upon a change from clear to caution or danger conditions for picking up the second stick relay, means effective when said secdnd stick relay is picked up for picking up the ilrst stick relay, holding means for the rst stick relay eiective only under caution conditions,

`holding means for the second stick relay effective only under danger conditions, and means for preventing the operation of said audible signal when the rst stick relay is energized.

24. Railway trailic controlling apparatus comprising train carried means continuously responsive to trackway conditions in advance of the train and arranged to visually indicate a clear vcondition and a -plurality of restrictive conditions tinuously responsive to a plurality \of different` trackway conditions and including a series of train carried stick relays, an audible signal, a manually operable acknowledging switch, a pickvup circuit for the first relay of said series including a contact of said switch, a pickup circuit for each of the remaining relays including' a front contact of the preceding relay of the series, a stick circuit for each relay, each controlled in accordance with a different trailic condition, and a circuit controlled by the last relay of the series for controlling the audible signal, whereby said signal is caused to sound when a change intrafc condition occurs unless said acknowledging switch is operated. p

26. Railway traiic controlling apparatus comprising a series of train carried relays continu- .ously responsive to trackway conditions in advance of the train and including a clearl vrelay energized to indicate a clear condition and a caution relay energized to indicate a restrictive condition of the track, an audible signal, a pair of stick relays, manually operable means for energizing the first relay of said pair, a pickup circuit Vfor the second relay of the pair closed when the first relay is energized, a stick circuit for the second relay of the pair closed only when the caution relay is energized and the clear relay is deenergiz'ed, a stick circuit for the first relay of the pair closed only whenV both the caution and clear relays are deenergized, a first circuit for controlling said audible signal including a contact of -the clear relay) and a second circuit for controlling said audible Signal including a contact of the second stick relay.

27. Railway traflic controlling apparatus comprising train carried means 4continuously responsive to trackway conditions in advance of the train and arranged to visually indicate clear, caution, or danger conditions of the track, an audible signal, means for preventing the operation of said signal under clear conditions, a first and a second stick relay, manually operable means effective under caution or danger conditions for picking up having a normal and a reverse position, a pickup circuit for the first relay ofy said series including 'a contact closed by the acknowledging switch in the reverse position, a pickup circuit for each of the remaining relays including a front contact of the preceding relay of the series, a stick circuit for each relay controlled in accordance with a particular trackway condition, means for deenergizing said magnet, and means for reenergizing 'said magnet effective when the last relay of said series `is energized provided said aclmowledging switch is' in its normal position.

29. Railway traiiic controlling apparatus comprising a series of train carried stick relays, manually operable means effective only under certain traiiic conditions to energize the first relay of said series, a pickup circuit for each of the remaining relays including a front contact of the preceding relay in said series, a stick circuit for each relay controlled in accordance with traiiic conditions, land governing meanscontrolled by said stick relays.

30. Railway traic controlling apparatus comprising a series of train carried stick relays, manually operable means effective only under certain trafc conditions to energize the first relay of said series, a pickup circuit for each of the remaining relays including a front contact of the preceding relay in said series, a stick circuit for each relay controlled in accordance with traffic conditions,

' and governing means controlled by the last relay lconditions to prevent operation of said signal when said relay is deenergized and when said cirfouit controller occupies its normal position, a pickup circuit for said relay closed under certainr other traiiic conditions when said circuit controller is reversed, a stick circuit for said relay including its own front contact for subsequently holding the relay closed under such other traiiic conditions, and means for preventing operation of the signal under such other trafiic conditions when the circuit controller occupies its normal position and when said relay is energized.

32. A railway cab signaling system comprising a vehicle, a normally energized train control relay thereon continuously responsive to trackway conditions, a visual cab signal comprising means effective when the train control relay is energized to indicate a clear track condition, and elective when the train control relay is deenergized to indicate a danger trackv condition, a magnet, an audible cab signal controlled by said magnet for indicating a change in track condition from clear to danger, and arranged to sound when the magnet becomes deenergized, a stick relay, a manually operable acknowledging switch having a normal and a reverse position, a pickup circuit for the stick relay adapted to be closed when said switch is reversed, a stick circuit for the stick relay including its own front contact and a contact closed only when the train control relay is deenergized, a first circuit for said magnet closed only when the train control relay is energized and said i switch is normal, and a second circuit for said magnet closed only when said stick relay is energized and said switch is normal.

33. A railway cab signaling system comprising a vehicle, a normally energized train control relay thereon continuously responsive to trackway conditions, a visual cab signal comprising means elective when the train control relay is energized to indicate a clear track condition and effective v when the train control relay is deenergized to indicate a danger track condition, a magnet, a normally closed circuit for said magnet controlled by a front contact of said train control relay, an audible cab signal controlled by said magnet for indicating a change in track condition from clear to danger and arranged to sound when the magnet becomes deenergized, a stick relay, a normally open circuit for said magnet controlled by a front contact of said stick relay, a. manually operable acknowledging switch having a normally closed contact in the circuits of said magnet and a lnormally open contact; and circuits for picking up and for holding said stick relay, each including a back contact of said train control relay, the circuit for picking up said stick relay also including the normally open contact of said acknowledging switch.

34. A railway cab signaling system comprising a vehicle, a normally energized train control relay theeron continuously responsive to trackway conditions, a. visual cab signal comprising a normally energized lamp controlled by a front contact of said relay for indicating a clear condition and a normally deenergized lamp controlled by a back contact of said relay for increasing a danger condition of the trackway, an audible cabsignal comprising a magnet and arranged to audibly indicate when the relay becomes deenergized vto thereby direct attention to the change in indication of said visual signal, said magnet being normally energized by a front contact of said relay, a manually operable acknowledging switch having a normal and a -reverse position, means for energizing said magnet to stop the sounding of said audible signal rendered effective if said acknowledging switch is reversed and is then restored to normal when the train control relay is deenergized, said means being eective to cause the sounding of said audible signal if said acknowledging switch is reversed when the train control relay is energized.

35. Railway traffic controlling apparatus comprising a train carried magnet valve, an audible signal controlled by said valve and arranged to sound when the magnet of said valve becomes deenergized, a train carried relay continuously responsive to trackway conditions and arranged to be energized only when traic conditions are safe, a manually operable circuit controller having a normal and a reverse contact, an acknowledging relay, a circuit vfor picking up said acknowledging relay including the reverse contact of said circuit controller, a stick circuit for said acknowledging relay including its own front contact and a back contact of said train control relay, a circuit for said magnet valve including a front contact of said train carried relay and the normal contact of said circuit controller, and a second circuit for said magnet valve including a front contact of said acknowledging relay and the normal contact of said circuit controller.

36. Railway traffic controlling apparatus comp rising a train carried audible signal, a normally deenergized relay, a manually operable circuit controller train carried means continuously controlled by current in the track rails and responsive to trackway conditions in advance of the vehicle, said means being eifective to prevent operation of said audible signal under clear track conditions provided said circuit controller occupies its normal position, a pickup circuit for said relay closed under other traffic conditions when said circuit controller is reversed, a stick circuit for said relay including its own front contact for subsequently holding the relay closed. under certain other traiic conditions, and means for preventing operation of the signal under said certain other tra'ic conditions when the circuit controller occupies its normal position and when said relay is energized.

37. Railway tramo controlling apparatus comprising train carried means continuously respon` sive to trackway conditions in advance of 4the train and arranged to visually indicate a clear condition and a plurality of restrictive conditions of the track, a magnet, means for causing said magnet to invariably become deenergized upon a change from a clear condition to a restrictive condition, manually operable means eiective under a restrictive condition to reenergize said magnet, and means invariably effective upon deenergization of said magnet to indicate a change in track conditions.

38. Railway traflic controlling apparatus comprising train carried means continuously responsive to trackway conditions`in advance of the train and arranged to visually indicate a clear condition and a plurality of restrictive conditions of the track, a normally energized magnet, means for causingv said magnet to invariably become deenergized upon a change from a clear condition to a restrictive condition, manually operable means effective under a restrictive condition to reenergize said magnet, means for causing said magnet when energized under a restrictive condition to again become become deenergized upon -a change from said restrictive indication to a diierent restrictive indication, and means effective upon deenergization of said magnet to indi- A cate-a change in track conditions.

,such relay operates.

said current at a predetermined rate, detecting means controlled by said current and arranged to deliver alternating current having a value which depends upon the value of the current in the track rails and a frequency which corresponds to its rate of variation, a relay repeating each 'alternation in polarity of the current delivered by said detecting means when such current has a predetermined value,and traffic governing means controlled by the alternations delivered by said relay and responsive tothe frequency at which such relay operates.

40. Railway traii'ic controlling apparatus comprising a stretch of railway track, means for supplying the track rails of the stretch with alternating current, means for periodically interrupting said current at a predetermined rate, detecting meanscontrolled by said current and arranged to deliver alternating current having a value which depends upon thevalue of the current in the track rails and a frequency which corresponds to its rate of interruption, a relay repeating each alternation in polarity of the current delivered by said detecting means when such current has a predetermined value, and traflic governing means controlled by the alternations delivered by said relay and responsive to the frequency at which 41. Railway traiiic controlling apparatus comprising a stretch of railway track, means for supplying the track rails of the stretch with alternating current, means for periodically interrupting said current at a predetermined rate, detecting means controlled by said current and arranged to deliver alterating current having a value which depends upon the value of the current in the track rails and a frequency which correspondsto its rate of interruption, means for repeating each alternation in polarity of the current delivered by said detecting means when such current has a predetermined value, means for rectifying the repeated alternations of current, and trafc governing means controlled by said rectified current.

42. In combination, a stretch of railway track, means for supplying the track rails of said stretch with alternating current which varies periodically at diiferent rates, a two-position relay responsive to each change in polarity of the current supplied thereto when such current exceeds a predetermined value, means for supplying the relay with current impulses of alternately opposite polarity of which the value and frequency correspond to the amount and rate of variation of the current in the track rails, to operate the relay at a frequency corresponding to said rate of variation, and traffic governing means selectively responsive to the frequency of operation of the relay.

43. Railway traiilc controlling apparatus comprising a stretch of railway track, means for supplying the track rails of the stretch with alternating current, means for periodically interrupting said current at any one of a plurality of predetermined rates, detecting means controlled by said current and arranged to deliver alternating current of a value which depends upon the value of the current in thel track rails and of a frequency which depends upon its rate of interruption, a relay for repeating each alternation in polarity of the current delivered by said detecting means when such current has a. predetermined the alternations delivered by said relay and selectively responsive to the frequency of operation of the relay.

44. In combination, a stretch of railway track, means for supplying the track rails of the stretch with alternating current periodically varied at different frequencies, an electron tube having a plate circuit including a source of direct current and a grid circuit including a xed negative voltage for reducing the current normally flowing in said plate circuit substantially to zero value, means for superimposing an alternating voltage varying at the frequencies of the track rail current upon said negative voltage, a transformer having its primary winding included in said plate circuit, and a relay connected with the secondary of such transformer and responsive to the polarity of the current supplied thereto.

45. In combination, a stretch of railway track, means for supplying the track rails of the stretch with alternating current periodically varied at different frequencies, a train carried transformer, means for supplying the primary of said transformer with unidirectional current of which the magnitude depends upon the value of the current in the track rails, said unidirectional current varying in magnitude at the frequency of variation of said track current, a two-position relay responsive to each change in polarity of the current delivered by the secondary ofv said transformer when such current exceeds a predetermined value, and train governing means selectively responsive to the frequency of operation of said relay.

46. In combination, a stretch of railway track, means for supplying the track rails of the stretch with periodically varying alternating current, a train carried transformer having a winding tuned to resonance at the frequency of such current,

means for energizing said transformer comprising an inductive circuit receiving energy from the track rails and tuned to resonance at said frequency, a first electron tube having a plate circuit and a grid circuit, means 'for applying to the grid circuit of said tube an alternating potential which varies as the electromotive force of said winding, 1.a second electron tube having a grid circuit coupled with the plate circuit of said first tube, a second transformer, a plate circuit for the second tube including the primary of said second transformer, a polarized relay connected with the #secondary of the transformer, and train governing means responsive to the frequency of operation of the relay.

l 47. In combination, a stretch ofrailway track, means for supplying the track rails of said stretch with alternating current, means .-.for periodically varying said current at any one of a plurality of different frequencies, receiving means comprising a plurality of resonant circuits which respond selectively to current in -the track rails having the frequency of said alternating current, detecting means adapted to deliver impulses of alternately opposite polarity of which the value and frequency corresponds to the amount and frequency of variation of the current delivered by said receiving means, a. plurality of traillc governing means each selectively responsive to a different one of said plurality of frequencies, and means controlled by each ol' said impulses for delivering a current impulse of corresponding polarity to each of said trame governing means.

48. In combination, a stretch of railway track, means for supplying the track rails of said stretch with alternating current, means for periodically interrupting said current at any one of a. plurality of different frequencies, receiving means vcomprising a plurality of resonant circuits which respond selectively to current in the track rails having the frequency of said alternating current, detecting means adapted to deliver impulses of alternately opposite polarity of which the value and frequency correspond to the amount and frequency of variation of the current delivered by said receiving means when energized by said interrupted alternating current, a plurality of traffic governing means each selectively responsive to a different one of said plurality of frequencies, and means controlled by each of said impulses for delivering a current impulse of corresponding polarity to each of said traillc governing means.

49. In combination, a stretch of railway track, means for supplying the track rails of said stretch with alternating current, train carried receiving means comprising a plurality of resonant circuits which respond selectively to current in the track rails having the frequency of said alternating current, detecting means controlled by said receiving means and adapted to convert periodically varying alternating current delivered by said receiving means into low frequency alternating current of which the value and frequency corresponds to the amount and frequency of such variation, a plurality of trafllc governing means controlled by said detecting means, each being selectively responsive to a different low frequency, and means controlled in accordance with traffic conditions for periodically interrupting the current in the track rails at one or another of said low frequencies to selectively control said trailic governing means.

50. In combination, a stretch of railway track, means for supplying the track rails of said stretch with periodically interrupted alternating current, receiving means selectively responsive to current in the track rails having the frequency of said alternating current, detecting Vmeans adapted to deliver impulses of alternately opposite polarity of which the value and frequency correspond to the amount and frequency of variation of the current delivered by saidreceiving means when energized by said periodically interrupted alternating current, a trame governing re- 

